A wedge connector for integrated circuits is known from U.S. patent application S/N 08/143, 005, filed Oct. 26, 1993. The wedge connector described therein comprises tapered fingers of conductive metal separated by an insulator. The tapered fingers are wedge-shaped, in that they are thinnest at their tips, so that they may more easily enter the space between adjacent legs of an integrated circuit (IC). A row of tapered wedges (i.e., tapered fingers) is assembled, and spaced apart to interdigitate with the legs of the IC. That is, the legs of the IC also form a row with an amount of inter-leg spacing between the legs along the direction of the row. The IC legs have sides that face each other along the direction of the row, and that are separated by the amount of the inter-leg spacing. By interdigitation we mean that the tapered fingers or wedges penetrate into the inter-leg space and contact the facing sides of the IC legs. Thus, the left-hand side of a wedge entering a particular inter-leg space will come into electrical contact with the right-hand side of the IC leg on the left of that inter-leg space, and the right-hand side of that wedge will come into electrical contact with left-hand side of the IC leg on the right of that inter-leg space. As the depth of penetration is increased the thicker parts of the wedge enter the inter-leg space, filling it completely and causing good wiping action and firm contact pressure between the sides of the IC legs and the sides of the wedges.
Within the row of wedges, the left-hand side of each wedge is electrically connected to the right-hand side of its neighboring wedge on the right, which, by implication means that the right-hand side of each wedge is also electrically connected to the left-hand side of its neighboring wedge to the right. This interconnectedness of the wedges in a row thereof produces a very desirable effect: if there are n-many legs on the IC and n+1 wedges in a row, then each leg of the IC is in electrical contact at two different places with two different wedges. This adds a robust reliability to the wedge connector.
FIG. 1 herein (which is also FIGS. 1 in the above mentioned Application) illustrates generally the technique described above. It is to be noted that the wedges interdigitate with the facing sides of adjacent legs of the IC, and that no attempt is made to produce contact with the outer faces of the legs of the IC; instead, the wedges pass between the legs.
As advantageous as the above described wedge connection technique is, experience with wedge connectors as described in the '005 Application has revealed occasional problems in their use. In brief, it would sometimes happen that certain wedges of the connector would not make electrical contact to the corresponding legs of the IC, unless uncomfortably high forces were used to press the connector into place. A further consequence is increased difficulty in safe removal. This not only raises the worry of extra mechanical stress on the IC, but also of unintentional damage to the wedge connector by a process that is much like what can happen when an IC is removed from a tight socket using the thumb and forefinger. "Dual in-line thumb" results when the IC slips in the grasp and its legs end up being pressed painfully into the thumb. (A simple extraction tool resembling a teeny tiny crowbar is actually preferred for the task of wedge probe removal; however it is unfortunately subject to not always being at hand when needed.) The wedges are not really sharp, and for a surface mount part with legs on 0.0197 inch (0.5 mm) centers they are close enough together that such an accident does not break the skin; but it can deform the wedges. This is more of an annoyance than a fatal result, as the wedges are usually readily reformed with the aid of an exacto knife blade under a low power microscope.
Two things appear to produce the difficulties described above. One is non-uniformity in the inter-leg spaces of the IC (arising from variations in the dam bar removal process). The other is the stiffness of the individual wedges, which prevents easy conformance with variations in the inter-leg spaces. The idea is that a small inter-leg space requires more force to penetrate, and can stop overall penetration of the wedge probe overall before all wedges have made contact. (It does not appear that there is any variation in the center-to-center spacing of the IC legs, just in the size of the gap remaining between adjacent legs when the dam bar is chopped out.)
Another problem has also been experienced, which is the scraping off of solder from the tinned legs of the IC by the tips of the wedges. This can result in a collection of solder debris at the tip of a wedge that shorts the two sides of that wedge together. This is quite undesirable, as the two sides of a wedge are associated with two different legs of an IC, and shorting the sides of a wedge together then shorts those legs together when the wedge connector is installed on the IC.
It would be desirable, then, to increase the compressibility and side to side flexibility of the wedges so that they may better comply with variations in the leg-to-leg gaps for the run of IC's, thus reducing the insertion force needed to ensure contact between the wedges and the sides of the legs.
It would also be desirable to eliminate the accumulation of solder debris from the tips of the wedges.
It would be further desirable if the increased compressibility and flexibility and the defense against solder debris made easier the initial alignment of the wedge connector with the IC, and made the obtaining of such interdigitation easier to recognize when obtained.